The protagonist is a young vagrant making a living by stealing. One day, he accidently summons a devil. Usually, in order to borrow its power, one must offer their soul in exchange.

However, this devil is quite an eccentric. It shows interest in Japanese entertainment, so it just gives the power to the protagonist and runs off to play around.

And thus, as someone who grows up in a rough environment, the protagonist is going to abuse this power and do whatever he wants.
Source: VNDB